Method of depositing particulate solid material on selected portions of a substrate



Aug. 3, 1965 P. D. PAYNE, JR

METHOD OF DEPOSITING PARTICULATE SOLID MATERIAL ON SELECTED PORTIONS OFA SUBSTRATE Flled June 25, 1956 IN VEN TOR. PHI/L a PflX/VE, Jk.

United States Patent 3,198,634 METHGD (BF DEPGEiKTlNG PARTICULATE 891.1%MATEREAL UN SELEtITEB PQRTEGNS OF A SUBSTRATE Paul D. Payne, in,Chalfont, Pa, assignor to Philco Corporation, Philadelphia, Pa, acorporation of Pennsylvania Filed Jinn-e 25, 1956, Ser. No. 593,682 14.Claims. or. 9635) This invention relates to methods for making screensfor cathode ray tubes and in particular to methods for producingimproved fluorescent screens for television image-reproducing tubes.

Cathode ray tubes presently employed for the reproduction of images ofscenes which have been televised in color are desirably constructed sothat their screens produce a light output of maximum brightness inresponse to the impingement of an electron beam thereupon. It is desiredto obtain a maximum brightness for several reasons among which may beenumerated the following. First, when a color television image isbright, the desaturating influence of ambient light and halation uponthe component colors of the image is less evident. Second, when theimage is bright there is no need for darkening of the viewing area topermit convenient viewing of the tube face. In fact it is believed that,if the viewing areas is made so dark as to present a sharp contrast tothe brightness of the image, the combined elfect is harmful to humanvision. constructing color television receivers of the projection typesince much of the light of the image on the cathode ray tube may be lostin transmission through the optical components of the projection system.

It is very diflicult to obtain images of the desired brightness whencertain types of color television display tubes, such as tubes of thewell-known so-called aperture mask type, are used. These tubes are veryinefiicient since most of the electrons in the three electron beamsproduced therein never reach the fluorescent screen because a perforatedmask of metal or other appropriate material is interposed between thethree electron guns and the screen. The screen contains phosphor dotsemissive of the three primary colors and the perforations of the maskare so aligned with the dots that they assist in insuring that each ofthe electron beams strikes only phosphor dots emissive of one of thethree primaries. In so doing, however, the aperture mask preventsapproximately 85% of the electrons emitted from the electron guns fromever reaching the fluorescent screen so that the brightness of the imageproduced is limited by the number of electrons which actually impinge onthe phosphor dots. The brightness of the image is also a function of thedensity of the phosphor material in the phosphor dots which are actuallystruck by electrons in the beam.

In color television display tubes other than tubes of the aperture masktype it is also desirable to increase the brightness of the imagesproduced, as, for example, in a tube of the type in which a plurality ofsets of strips of phosphor materials respectively emissive of the threeadditive primary color are disposed on the internal face plate of thetube. In this type of tube a single writing beam may be produced whichmay be deflected in scanning paths either parallel to, or transverse tothe direction in which the phosphor strips individually extend. Thesingle beam is modulated in intensity by signals which represent colorsemitted by the strip on which the beam is scanning at any given instant.tubes of this general construction in which substantially all of theelectrons emittedfrom the cathode strike the screen, to achieve amaximum image brightness for man of the reasons previously given. a

Third, a bright image is especially helpful in It is desirable, even inMaximum image brightness is sought for in still other types of cathoderay tubes, such as ones containing a screen which comprises a number ofsets of mutually interleaved phosphor strips and a plurality of spacedelectrodes intermediate the screen and an electron gun, said electrodesbeing arranged so that they are parallel to the phosphor strips. Asingle writing beamis deflected over the screen thereof in a pluralityof scanning paths which are usually substantially parallel to the spacedelectrodes. The beam is additionally deflected transversely to thescanning paths by potentials applied to the latter electrodes whichcause the beam to impinge on selected ones of the phosphor strips atselected intervals.

In the above-mentioned types of image-reproducing tubes, as well as inother single or plural beam varieties of display devices, given acertain value of beam current an increase in the density of thephosphors on the screens thereof would materially assist in producing anoptimum light output therefrom. One known way of achieving.

greater phosphor density is to form the screen by depositing each set ofphosphor elements in several layers; Whenever greater phosphor densityis achieved by resort' of phosphors for increasing phosphor density. Oneof these methods involves photographic processes in which photosensitivecoatings or emulsions are exposed to the desired light pattern, thedesired phosphor material is next deposited on the photographicemulsion, and then the unexposed portions of the phosphor material,together with the phosphor particles adhering thereto, are washed away,whereupon the process is repeated for the second coating. A morecomplete description of such a process is contained in my copending US.application, Serial No. 376,345, filed August 25, 1953, now US. PatentNo. 2,950,193. In order to wash the unexposed portions away, it hashitherto been customary to remove the screen from the position in whichit was exposed to the particular light pattern involved. After the firstwashing, the screen is recoated with the photosensitive material, dried,and then returned to its original position for re-exposure to the samelight pattern. Accuracy and precision of a very high order are requiredin order to reposition the screen of the tube,

on which the first of two layers of phosphor materials has beendeposited, exactly in the same position for exposure prior to theapplication of the second layer of phosphors.

If the light pattern projected upon the photosensitive emulsionpreliminary to the application of the second layer of phosphors is notin exact register with the phosphor pattern produced by the firstapplication, the phosphor strips produced may have irregular widths.

Since the multiple application of phosphors as a means of producingscreens possessing greater phosphor density in costly and demands a highdegree of precision, new

approaches to the problem of increasing phosphor density have beenattempted. Before embarking upon these new approaches a study of thefeatures of the previous method and materials used therein was made. Inparticular, a study was made of the process of depositing phosphors andother screen elements in which a light pattern is projected, from therear, onto a photosensitive layer containing ammonium dichromate as thephotosensitizing 7 agent.

Patented Aug. 3, 1965 In order to obtain the best results possible witha photosensitive layer containing ammonium dichromate, it is important,first, that the layer should adhere very well to the internal surface ofthe particular substrate used, as for example, to the internal surfaceof the glass faceplate of a cathode ray tube. Unless there is goodadhesion of the photosensitive material to the substrate, there is apossibility that, when the unexposed portions thereof are washed awaytogether with the phosphor material deposited thereupon in subsequentwashing operations, some of the exposed portions of the :hotosensitivematerial and the phosphor material in contact therewith may also bewashed away. Good adhesion of the photo sensitive material to thesubstrate is a function of the hardness of the photosensitive materialwhen fixed by exposure thereof to the form of illumination to which thematerial is sensitive.

Another desideratum in using such a photosensitive material is that,when the photosensitive material is deposited upon the substrate, thehardness of selected portions of the rear surface thereof (i.e., thesurface closest to the light source) be such, after exposure, that themaximum number of phosphor particles adhere thereto. This condition isattained when the rear surface of th photosensitive material is somewhatsofter than the front surface after exposure.

- It is extremely difiicult, however, when using photosensitizingmaterials which contain ammonium dichromate as the photosensitizingagent, to produce on the substrate a layer of the photosensitivematerial whose front surface, after exposure, is rendered relativelyhard and whose rear surface is rendered somewhat softer than the frontsurface thereof, but which is rendered harder and less soluble than theportions of the layer which are not exposed.

One reason for this difiiculty is that the ammonium dichromate issomewhat orange-yellow in color and the layer of photosensitive materialbecomes colored thereby. Therefore, when the photosensitive layer isexposed from the rear the particles of ammonium dichromate near the rearsurface of the photosensitive layer act like a number of minuteorange-yellow filters which absorb a large proportion of light in theultra-violet region, i.e., light having a Wave length of about 3,650angstroms, this being light of the region to which the layer is mainlyresponsive. Thus only a small amount of ultraviolet light is transmittedto the front surface of the photosensitive layer. As a result the frontsurface of the layer is rendered semi-hard because it is relativelyunderexposed whereas the rear surface is rendered very hard because itis relatively overexposed. This is a condition which is just theopposite of the one desired. Consequently the front part of thephotosensitive layer does not adhere to the substrate so Well and thereis a possibility that it and the phosphor material later deposited incontact therewith may be dislodged from the substrate in subsequentwashing operations. On the other hand, since the rear surface of theexposed portions of the photosensitive ,layer has been made hard byexposure, fewer phosphor particles will adhere thereto than if it weresoft. If increased phosphor density is desired, the customary techniqueof multiple phosphor applications with its attendant disadvantages maythen be resorted to.

Accordingly, it is a primary object of my invention to provide animproved method of manufacturing screen structures for cathode raytubes.

It is another object of my invention to provide an improved method ofmanufacturing the screen structures of cathode ray tubes used forreproducing images televised in color.

Still another object of my invention is to provide a method formanufacturing improved screen structures for obtaining brighter imagesin color televsion display tubes.

Another aim of the invention is to reduce the cost of manufacturingscreen structures-for cathode ray tubes used for reproducing images ofscenes televised in color.

A further object of my-invention is to provide a method formanufacturing screen structures for cathode ray tubes for colortelevision receivers in which elements previously formed are not washedaway in subsequent steps of the manufacturing process.

My invention is based on the realization that, if the rear surfaceregion of the photosensitive layer is made somewhat less photosensitiveprior to exposure than the front surface region, the rear surface regionwill be rendered less hard than the front surface region when exposed.In order to produce a gradient of photosensitivity throughout thephotosensitive layer, I have taken advantage of the fact that thephotosensitivity of any portion of the layer depends on theconcentration of photosensitive particles therein.

Accordingly the layer is so prepared prior to exposure that there is agreater concentration of the photosensitizing substance toward the frontsurface than toward the rear surface thereof. When the photosensitivesubstance is so distributed, the front surface area receives and absorbsmore of the actinic rays from the source of illumination than hashitherto been possible so that it becomes fixed to a fairly high degreeof hardness, and thus its adhesion to the substrate is enhanced. Sincethere are fewer particles of the photosensitizing substance toward therear surface of the layer, fewer of the actinic rays will be absorbedtherein and the rear surface area will not be fixed to the same degreeof hardness as is the front surface area. As a result, the rear surfacearea is rendered relatively soft so that, after exposure, more phosphorparticles can adhere thereto.

I11 order to produce a photosensitive layer having the -esired gradientof photo-sensitivity according to my invention the photosensitive layeris deposited, prior to exposure, on the substrate as has previously beencustomary. Then. a solvent for the photosensitizing substance of thephotosensitive layer is applied to the rear surface of the layer. Thissolvent causes the particles of the photosensitizing substance near therear surface to enter into solution. The applied solvent, together withthe particles of the photosensitizing substance dissolved therein, isthen drawn off. When the solvent has been drawn off, the remainingphotosensitive layer has a greater concentration of photosensitizingsubstance near the front surface than near the rear surface. Next theprepared layer is exposed to the desired pattern of light, then coatedwith selected phosphor or other materials, and finally washed in thecustomary manner. It has been found that, by employing the processaccording to my invention, the density of the phosphor material in thephosphor elements deposited in one application approximates thatachieved by convention- 211 double application techniques. It is thuspossible to produce at a smaller cost a cathode ray tube whose screenwill produce images of the desired brightness.

FIGURE 1 is a schematic and perspective view of a rear-projectionphotographic deposition system in which my invention may be used; and

FIGURES 2A to 2F inclusive are a six-pant schematic and sectionalrepresentation of the steps of a photographic deposition process whichembodies my invention.

Solely for convenience in exposition, the invention will be explained inconnection with a color television cathode ray tube of a type previouslymentioned, i.e., one having a number of strips of phosphor materialsemissive of the additive primary colors, i.e., red, green and blue,arrayed in a spaced-apart and substantially parallel relation on thefaceplate of the tube. This type of screen may be scanned by a singleWriting electron beam which is modulated in intensity by signalscorresponding to the color of the element impinged upon. In some formsanother electron beam having low current may be provided which isdeflected in unison with the writing beam and which is caused to impingeupon portions of the screen having secondary-emission ratios, forexample, which differ from the secondary-emission ratios of otherportions thereof. As a result, so-called indexing signals are generatedwhich are used to coordinate the modulation of the writing beam with theposition thereof. The construction of such a tube is described in moredetail in the US. Patent No. 2,725,421 issued November 29, 1955 to S. F.Valdes.

In order to produce the phosphor strips of such a tube on the faceplate,a rear-projection photographic deposition method, such as described inthe co-pending U.S. application of M. Sadowsky and S. Parsons, SerialNo. 488,219, filed Februray 4, 1954, now U.S. Patent No. 2,870,010 isoften used. In this method, which is illustrated in FIGURE 1, the innersurface of the faceplate 11 of a cathode ray tube is coated with a layer18 of a photosensitive material. A photosensitive layer which has provedvery useful in this process is one produced by depositing on thefaceplate 11 a solution containing ninety parts by volume of a stocksolution comprising 600 cc. of water, 200 cc. of a denatured alcoholsuch as that sold under the trademark Solox, grams of a polyvinylalcohol such as that sold under the trademark Elvanol 52-22, and 1%grams of ammonium dichromate to which ten additional parts by volume ofSolox are added. The ammonium dichromate is the photosensitizingsubstance in this solution and impart-s an orange-yellow color thereto.This solution is flowed onto the inner surface of the faceplate 11 andis dried at room temperature unit it be comes a layer 18 as shown inFIG. 2A resembling dried sheet gelatine in its consistency. When thesolution is dried the sensitizing substance, ammonium dichromate, isdistributed uniformly throughout the layer 18 in the form of a number ofminute particles 19. When the ammonium dichromate particles are struckby actinic ray, i.e., rays of light in the ultra-violet region of thespectrum (around 3960 angstroms), the ammonium dichromate is broken downinto compounds which include chromium oxides which cause the portions ofthe layer in proximity thereto to become hard and relatively insolublein water.

In accordance with the present invention the concentration of ammoniumdichromate particles 19 toward the rear surface of the photosensitivelayer 18 is made less dense than elsewhere in the layer by flowing ontothe rear surface of the dried photosensitive layer 18 additional amountsof the aforementioned Solox. The minute particles 19 of ammoniumdichromate within the layer are dissolved by the additional Solox,whereas the polyvinyl alcohol component of the layer adsorbs some of theadditional Solox and is swollen somewhat thereby. The excess Solox andthe ammonium dichromate dissolved therein is then drawn oif. Thephotosensitive layer is then dried so that the Solox, which has swollenthe polyvinyl alcohol component of the layer, is evaporated thereform.The photosensitive layer 18 now has a greater concentration of thephotosensitizing ammonium dichromate particles 19 near the surfacethereof closer to the substrate than it does near the rear surface ofthe layer 18 as shown in FIG. 2B.

The layer 18 has now been prepared for the conventional steps ofexposure and phosphor deposition such as have hitherto been known in theart. A source of light, indicated schematically (in FIG. 1) at thenumeral 12, provides light rays which pass through the grill 13 whichhas a plurality of alternately opaque andtransparent sections 14 and 16respectively. Light rays transmitted through the transparent sections 16are focused upon the prepared layer 18 by an optical system indicated atthe numeral 15. When the image of the grill 13 is projected on theprepared photosensitive layer 18, those portions of the latter on whichlight transmitted through the transparent portions 16 falls, such as theportion 20 shown in FIG. 2C, become fixed or harder than the otherportions thereof which are unexposed such as the portions 21. In theexposed portion 24) there is a greater concentration of thephotosensitizing particles 19 closer to the faceplace 11 than there istoward the rear surface so that the front region of the portion 211 willbe rendered harder than the rear region thereof.

After exposure, a slurry of a desired phosphor material 22 is flowedonto the rear surface of both the eX- posed and unexposed portions 20and 21 of the photosensitive layer 18 as shown in FIG. 2D. This slurryis then dried and the screen is then washed with water. It ischaracteristic of the photosensitive layer 18 that the portions 21thereof which have not been exposed to light are very soluble in waterwhereas the portions 20 which have been are relatively insolubletherein. Therefore, when subjected to the washing action of water, theunexposed portions 21 of the layer 18, together with the portions of thephosphor 22 in contact therewith, will be washed away leaving only theexposed portions 20 and the portions of the phosphor incontactftherewith as shown in'FIG. 2E. 7

If it is desired to lay down phosphor strips emissive of other colors inthe spaces formerly occupied by the unexposed portions 21 of the layer18, the foregoing process is repeated, i.e., a photosensitive layer isfirst applied to the substrate and to' rear surface of the exposedportions 20, then the layer is dried, then additional Solox is appliedand drawn off to remove part of the ammonium dichromate toward the rearsurface of the new layer of photosensitive material, the preparedphotosensitive layer is again dried and then exposed to the desiredpattern of light rays, the additional phosphor material is deposited onthe rear surface of the prepared photosensitive layer, the phosphorslurry dried and the screen subjected once again to a wash in water. Asmany different sets of phosphor materials as is desired may be depositedin the preceding manner to form the screen. 'When'all the elements ofthe screen have been deposited in this manner, the residual layer 18 isremoved, usually by subjecting the screen to a high heat in a baking outoperation leaving the phosphor strips in contact with the faceplate asshown in FIG. 2F.

It has been found that, when photosensitive layers prepared inaccordance with my invention are used in making screens, much greaterphosphor density per given unit of area of the phosphor element isobtained. In fact, phosphor densities comparable to those obtained bythe customary double application procedure have been attained.Previously, as many as twenty-four different steps were required (priorto baking-out the screen) to lay down three different sets of phosphorelements on the faceplate, each set of phosphor elements being depositedtwice. By using the process according to my invention as describedherein, three sets of phosphor elements may be deposited on thefaceplate in approximately fifteen steps rather than the approximatelytwenty-five steps required to arrive at the same point in themanufacture of this screen according to the prior method. Theelimination of nine steps helps to cut down the cost of production ofcolor television tubes employing such screens. Also, since only half asmany layers of photosensitive materials are used there is less waste ofthis material. Furthermore, less phosphor material is wasted since theexcess phosphor material is washed away only three times rather than sixtimes as in the previous process.

-The invention is also applicable to the deposition of materials otherthan phosphors. It has been stated above that, in tubes such as thosehaving phosphor strips arranged as shown in FIG. 1, the screen thereofmay also contain portions having different secondary-emission responsesto the impingement of the indexing beam thereupon. The portions having agreater secondary-emission ratio may consist of vertical strips of amaterial such as MgO, for example, which are arranged in a predeterminedspatial relation to selected ones of the phosphor strips. The density ofthe indexing strips is one factor in determining the aplitude of theindexing signals produced.

amass-s It is often desirable to make the amplitude of the indexingsignals large so as to facilitate detection of them. By using theprocess according to my invention, a single application of the MgO willusually suffice to produce the desired density of MgO and hence thedesired amplitude of indexing signals.

The invention may also be used to lay down the socalled guard lineswhich. are sometimes incorporated in the screens of such tubes. Theguard lines are strips of an opaque and substantially non-reflectivematerial disposed between adjacent ones of the phosphor elements intubes having screens such as shown in FIG. 1. These guard lines help toprevent desaturation of the colors of the reproduced image by cuttingdown halation and adverse effects of ambient light falling on thefaceplate of such tubes. They also facilitate the mass fabrication oftubes. A fuller explanation of guard lines and methods of obtaining thesame are contained in the co-pending US. patent application of Frank I.Bingley entitled Electrical Systems, Serial No. 551,648 filed December7, 1955, now US. Patent No. 2,842,697. The guard lines are mosteffective when they are completely opaque. Their opacity is somewhatdependent upon the density of the material used. Therefore, if the guardlines are deposited according to the process hereinbefore described, anoptimum density of the opaque material can be achieved.

I It will be understood that still other applications of the processesaccording to the diverse forms of my invention described herein willoccur to those skilled in the art. Consequently, I desire the scope ofthis invention to be limited only by the following claims.

What I claim is:

1. In the method of depositing particulate solid material on selectedportions of a substrate, comprising the steps of 2 forming on saidsubstrate a layer made of a composition containing a photosensitizingsubstance, said photosensitizing substance impeding the transmission ofradiant energy of a given form through said composition and saidcomposition having a hardness which increases and a solubility in agiven solvent which decreases, in response to exposure of saidcomposition to radiant energy of said given form, by respective amountsdirectly dependent on both the concentration of said photosensitizingsubstance and the quantity of radiant energy of said given form to whichsaid composition is exposed;

exposing those regions of said layer overlying said selected portions ofsaid substrate to radiant energy of said form throughout the thicknessof said layer, said exposure being sufficient to render said regionssubstantially less soluble in said given solvent than the unexposedregions of said layer;

7 depositing said particulate material on at least the exposed portionsof the surface of said layer opposing and remote from said substrate,

and washing said layer with said given solvent sufficiently to removeselectively both said unexposed regions of said layer and particles ofsaid material deposited on said unexposed regions,

the improvement which comprises forming said layer so that the theconcentration of said photosensitizing substance therein decreases alongat least part of its Thickness from a given value adjacent saidsubstrate to a lesser value adjacent said opposing surface, whereby allparts of said layer can be hardened approximately uniformly even thoughthe part thereof adjacent said opposing surface is exposed to moreradiant energy of said given from than other parts thereof.

2. A method according to claim 1, wherein said step of forming saidlayer comprises the steps of coating said substrate with saidcomposition, applying to the surface of said coating which opposes andis remote from said S substrate a solvent for said photosensitizingsubstance, thereby to dissolve a part of said photosensitizing substancein said coating, and removing from said coating a solution comprisingsolvent applied to said coating and photosensitive material dissolvedtherein.

3. A method according to claim 1, wherein said exposure step is carriedout so that said radiant energy enters into said layer at said opposingsurface.

4. A method according to claim 1, wherein said photosensitizingsubstance is a dichromate salt.

5. A method according to claim 1 of forming a screen structure for acathode ray tube, wherein said particulate solid material is a substanceemissive of radiation in response to electron impingement thereon andsaid substrate is composed of a substance transmissive of saidradiation.

6. A method according to claim 1 of forming a screen structure of acathode ray tube, wherein said particulate solid material is a substanceemissive of secondary electrons in response to electron impingementthereon.

7. A method according to claim 1, wherein said composition principallycomprises a polyvinyl alcohol and said photosensitizing substance isammonium dichromate.

3. A method according to claim 7, wherein said given solvent is water.

9. in the method of depositing particulate solid material on selectedportions of a substrate, comprising the steps of:

forming a photosensitive layer on said substrate by flowing onto saidsubstrate a mixture containing a photosensitizing substance and a firstsolvent therefor and drying said mixture, said photosensitizingsubstance impeding the transmission of radiant energy of a given formthrough said dried mixture and said dried mixture having a hardnesswhich increases and a solubility in a second solvent which decreases, inresponse to exposure of said dried mixture to radiant energy of saidgiven form, by respective amounts directly dependent on both theconcentration of said photosensitizing substance and the quantity ofradiant energy of said given form to which said dried mixture isexposed;

exposing those regions of said layer overlying said selected portions ofsaid substrate to radiant energy of said form throughout the thicknessof said layer, said exposure being sufficient to render said regionssubstantially less soluble in said second solvent than the unexposedregions of said layer;

depositing said particulate material on at least the exposed portions ofthe surface of said layer opposing and remote from said substrate,

and washing said layer with said second solvent sufiiciently to removeselectively both said unexposed regions of said layer and particles ofsaid material deposited on said unexposed regions,

the improvement which comprises the additional steps,

performed before said exposing step, of flowing onto said opposingsurface of said layer a quantity of said first solvent sutficient todissolve a given amount of said photosensitizing substance from the partof said layer adjacent said opposing surface, removing from said layermost of said quantity of first solvent together with saidphotosensitizing substance dissolved therein, and redrying said layer,whereby all parts of said layer can then be hardened approximatelyuniformly even though the part thereof adjacent said opposing surface isexposed to more radiant energy of said given form than other partsthereof.

I A method according to claim 9, wherein said particulate matter isdeposited by flowing a slurry thereof over said mixture and drying saidslurry.

ILThe method according to claim 9 wherein said photosensitizingsubstance is ammonium dichromate,

9 10 wherein said first solvent is a denatured alcohol, and 2,683,7697/54 Banning. wherein said second solvent is water. 2,747,997 5/56 Smithet a1.

12. A method according to claim 11, wherein said 2,790,107 4/57 Bradley.mixture consists principally of a polyvinyl alcohol. 2,950,193 8/60Payne.

13. The method according to claim 11 wherein said 5 FOREIGN PATENTSparticulate SOlld material IS an electron-sensitive phosphon 6,368 5/85Great Britaln.

14. The method according to claim 13, including the OTH REFERENCES fi ggi z g. ii Friedman, History of Colored Photography, 1944-The p or maarms on Se ece p0 ions 0 Sal 10 American Photographic Publishing Co.,Bostonpages strate.

References Cited by the Examiner NORMAN G. TORCHIN, Primary Examiner.

UNITED STATES PATENTS 15 MILTON STERMAN, PHILIP E. MANGAN, HAROLD1,785,635 12/30 Lebedenko 96-35 N. BURSTEIN, WILLIAM B. KNIGHT,Examiners.

2,370,330 2/45 Smith et a1. 96-49

1. IN THE METHOD OF DEPOSITING PARTICULATE SOLID MATERIAL ON SELECTEDPORTIONS OF A SUBSTRATE, COMPRISING THE STEPS OF: FORMING ON SAIDSUBSTRATE A LAYER MADE OF A COMPOSITION CONTAINING A PHOTOSENSITIZINGSUBSTANCE, SAID PHOTOSENSITIZING SUBSTANCE IMPEDING THE TRANSMISSION OFRADIANT ENERGY OF A GIVEN FORM THROUGH SAID COMPOSITION AND SAIDCOMPOSITION HAVING A HARDNESS WHICH INCREASES AND A SOLUBILITY IN AGIVEN SOLVENT WHICH DECREASES, IN RESPONSE TO EXPOSURE OF SAIDCOMPOSITION TO RADIANT ENERGY OF SAID GIVEN FORM, BY RESPECTIVE AMOUNTSDIRECTLY DEPENDENT ON BOTH THE CONCENTRATION OF SAID PHOTOSENSITIZINGSUBSTANCE AND THE QUANTITY OF RADIANT ENERGY OF SAID GIVEN FORM TO WHICHSAID COMPOSITION IS EXPOSED; EXPOSING THOSE REGIONS OF SAID LAYEROVERLYING SAID SELECTED PORTIONS OF SAID SUBSTRATE TO RADIANT ENERGY OFSAID FORM THROUGHOUT THE THICKNESS AND SAID LAYER, SAID EXPOSURE BEINGSUFFICIENT TO RENDER SAID REGIONS SUBSTANTIALLY LESS SOLUBLE IN SAIDGIVEN SOLVENT THAN THE UNEXPOSED REGIONS OF SAID LAYER; DEPOSITING SAIDPARTICULATE MATERIAL ON AT LEAST THE EXPOSED PORTIONS OF THE SURFACE OFSAID LAYER OPPOSING AND REMOTE FROM SAID SUBSTRATE, AND WASHING SAIDLAYER WITH SAID GIVEN SOLVENT SUFFICIENTLY TO REMOVE SELECTIVELY BOTHSAID UNEXPOSED REGIONS OF SAID LAYER AND PARTICLES OF SAID MATERIALDEPOSITED ON SAID UNEXPOSED REGIONS, THE IMPROVEMENT WHICH COMPRISESFORMING SAID LAYER SO THAT THE THE CONCENTRATION OF SAIDPHOTOSENSITIZING SUBSTANCE THEREIN DECREASES ALONG AT LEAST PART OF ITSTHICKNESS FROM A GIVEN VALUE ADJACENT SAID SUBSTRATE TO A LESSER VALUEADJACENT SAID OPPOSING SURFACE, WHEREBY ALL PARTS OF SAID LAYER CAN BEHARDENED APPROXIMATELY UNIFORMLY EVEN THOUGH THE PART THEREOF ADJACENTSAID OPPOSING SURFACE IS EXPOSED TO MORE RADIANT ENERGY OF SAID GIVENFROM THAN OTHER PARTS THEREOF.